JPH0756459B2 - Mass flow meter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mass flow meter for measuring a mass flow rate of a measurement fluid using a Karman vortex.

(Prior Art) It has long been known that when an object is placed in a fluid, vortices are alternately and regularly generated from both rear surfaces of the object and flow in a vortex row downstream. This vortex street is called Karman vortex street, and the number of vortices generated per unit time (generation frequency) is proportional to the flow velocity of the fluid. Therefore, a vortex generator is placed in the conduit that guides the fluid to be measured, and the vortex generator generates a vortex that is proportional to the flow velocity. The lift change caused by the vortex is detected by a piezoelectric element, strain gauge, sensor such as capacitance or inductance. A vortex flowmeter for detecting and measuring only the frequency of a detection signal to measure the flow velocity and flow rate of a fluid has been put into practical use. by the way,
Generally, the flow rate to be known is often the mass flow rate not only in the process of making a chemical change, but also in trading. When the fluid to be measured is gas or steam, its density greatly changes depending on temperature and pressure, and even when it is liquid, its density considerably changes depending on temperature. Therefore, the mass flow rate is measured by installing the vortex flowmeter in parallel to measure temperature and pressure, or by measuring the density with a density meter. However, it is complicated and expensive to use the density meter and the vortex flowmeter, and the combination of the temperature or pressure gauge and the vortex flowmeter is not only complicated and expensive.
Since it is difficult to measure the liquid temperature, the accuracy and responsiveness are poor.

By the way, as shown in FIG. 10, when the vortex generator 2 is arranged in the pipe line 1 and the measurement fluid is flown in the pipe line 1, the average drag force F _D acting on the vortex generator 2 and the variable lift force F _L The pressure loss ΔP generally has a relationship represented by the following equation.

However, C _D ; drag coefficient C _L ; fluctuating lift coefficient C _p ; pressure loss coefficient ρ; density V; flow velocity (1) and (2)
P.79, P.87 21 Kutta Zhukovsky's Theorem by Ichiro Tani, Iwanami Shoten. Further, (3) is derived from the loss due to separation of the boundary layer from the vortex generator (generation of Karman vortex).

Now, the average drag force F _D, variation lift F _L, the pressure loss ΔP is the drag coefficient C _D, variation coefficient of lift C _L, if the pressure loss coefficient C _p is a constant, it is proportional to the pV ^2, the vortex frequency (However, St: Strouhal number, d: Diameter of vortex generator 2, By dividing equations (1), (2) and (3) by
V is obtained.

pV ² detector and by dividing the V detector [rho · V ² / V
The calculation of the mass flow rate of = ρV is also a technique that has been generally performed conventionally, as described in the flow rate measurement handbook, edited by Hiroo Kawada, P.344, published by Nikkan Kogyo Shimbun.

In the vortex flowmeter, a well-known example of this type is the West German patent.
DE3032578C2 "Dynamic fluid density independent method and device (Mass flow rate measurement by vortex flowmeter)" is available to detect fluctuating lift as strain of strain gauge attached to vortex generator. Alternatively, the mass flow rate is obtained by detecting the torque generated in the vortex generator by a spring, or by detecting the drag force by installing a Pitot tube in front of the vortex generator and dividing the drag force with the vortex frequency.

In Japan, the actual measurement device 54-174359 “Measurement device using Karman vortex” is also equipped with a diaphragm capacity detector on the upstream and downstream sides of the vortex generator to detect the drag force F _D from the DC component of the capacity change. There is a method in which the mass flow rate is obtained by detecting and dividing the eddy frequency from the AC component.

Further, Japanese Patent Application Laid-Open No. 57-61916 “Measuring device using Karman vortex” shows an example in which a variable lift is detected and divided by the vortex frequency.

Hereinafter, JP-A-57-61916 will be described.

FIG. 11 is an explanatory view of the construction of the Japanese Patent Laid-Open No. 57-61916. In the figure, 1a is a pipe through which a measurement fluid flows, 2a is a columnar vortex generator vertically inserted into the pipe 1a, and both ends thereof are fixed to the pipe 1a. The main body 21a of the vortex generator 2a is made of stainless steel or the like, and has a cross-sectional shape such as a trapezoid that causes a Karman vortex street in the measurement fluid and stably enhances the change in lift. The top 22a of the vortex generator 2a is made of stainless steel or the like, has a recess 23a, and is integrally formed with the main body 21a by welding or the like. Reference numeral 41a denotes an element body made of a piezoelectric element, which is sealed in the recess 23a of the vortex generator 2a with an insulating material 3a such as glass and is formed integrally with the vortex generator. In addition, the element body 41
a has a disk shape and is arranged so that its center coincides with the neutral axis of the vortex generator 2a. Further, in the element body 41a, electrodes 42a, 43a, 44a, 45a are symmetrically divided into left and right sides on the front and the back, respectively, as shown in FIG.
The portion sandwiched by 2a and 43a forms the first piezoelectric sensor 46a, and the portion sandwiched by the electrodes 44a and 45a forms the second piezoelectric sensor 47.
form a. The electrodes 42a and 45a and the electrodes 43a and 44a are connected to each other so that the charges generated in the first and second piezoelectric sensors 46a and 47a are differential, and the leads 42a and 49a are connected to the electrodes 42a and 44a, respectively. Penetrates through the insulating material 3a and is taken out to the outside. 8a is a detection signal processing circuit, and the piezoelectric sensor 46
The AC charge q detected at a, 47a is converted into an AC voltage e. 9
a is a comparator for converting the AC voltage e into a pulse signal P of a constant level.
It is for converting to. 10a is an F / V converter,
The pulse signal P output from the comparator is converted into a DC voltage E ₁ proportional to its frequency. 11a is a rectifying / smoothing circuit, which is an alternating voltage e
Is rectified and smoothed, and converted into a DC voltage E ₂ proportional to its amplitude. 12a is an arithmetic circuit performs the desired operation on the output E _1, E ₂ of the F / V converters 10a and the rectifying smoothing circuit 11a, is for taking out the signal related to the density or mass flow rate of the fluid at its output .

In the present invention thus configured, when the measurement fluid flows in the conduit 1a, the vortex generator 2a generates a Karman vortex and undergoes a lift change due to the generation of the vortex. Vortex generator
When 2a is subjected to a change in lift, a stress change occurs in the opposite direction across the neutral axis as shown in the figure. The change in stress generated in the vortex generator 2a is transmitted to the element body 41 integrally attached to the vortex generator 2a by the insulating material 3a. Therefore, in the first and second piezoelectric sensors 46a and 47a, changes in the amount of electric charge in opposite phases occur corresponding to changes in the lift force. And the piezoelectric sensor 46
The amount of electric charge generated in a and 47a is taken out differentially, and the lead wire 4
An alternating charge q is generated between 8a and 49a. The alternating charge q is converted into an alternating voltage e by the detection signal processing circuit 8a. If the frequency of the AC voltage e is taken out through the comparator 9a and the F / V converter 10a, a voltage E ₁ proportional to the vortex frequency f, that is, the flow velocity can be obtained as in a general vortex flowmeter as shown in equation (4).

E ₁ = K ₁ V (4) However, K ₁ is a proportional constant. On the other hand, if the amplitude of the AC voltage e is extracted via the rectifying / smoothing circuit 11a, the output E ₂ of the rectifying / smoothing circuit 11a is Given by the formula.

E ₂ = K ₂ ρV ² (5) However, K ₂ is a proportional constant The output Eo is Becomes If the cross-sectional area of the conduit 1a is S, the mass flow rate Qm is given by Qm = ρVs (7), so Eo is And the signal becomes proportional to the mass flow rate.

Further, in the arithmetic circuit 12a, if E ₁ is squared and then E ₂ is divided, the output Eo is Therefore, a signal proportional to the fluid density can be obtained.

The above is an idea that holds under the assumption that the variable lift coefficient C is constant. Similarly, in West German Patent DE 3032578 C2, it is also necessary that the variable lift coefficient C be constant.

(Problems to be solved by the invention) However, now, the fluctuation lift _FL , drag due to Karman vortex, drag
F _D and vortex frequency output (volume flow rate) F F _V = K ₁ V where F _L ; Fluctuating lift F _D ; Drag force F _V ; Vortex frequency output (volume flow) C _L ; Fluctuating lift coefficient C _D ; Drag coefficient ρ; Density V; Velocity d; Flow of vortex generator Opposite diameter D; pipe diameter K ₁ ; constant therefore K ₃ in equation (6) is Becomes

Here, the variable lift coefficient C _L is, for example, the drag coefficient C _{D as} shown in FIG. 13 or the Strouhal number as shown in FIG.
Even when St is constant, it is not constant as shown in FIG. (Figures 13 to 15 are based on Toshio Kobayashi's "Fluid Force Acting on Bluff Body" magazine "Production Research", 24th.
Volume 1, Issue 1, Institute of Industrial Science, University of Tokyo, Figure 1, Figure 7, Figure 8
Was quoted. 11) In the conventional example of FIG. 11, the detection signal processing circuit 8a includes a filter circuit for surely detecting the vortex frequency, as used in the vortex flowmeter.
The raw signal from the sensor is generally superposed with high-frequency and low-frequency noise due to turbulence present in the fluid. In particular,
High frequency noise becomes noticeable at low flow velocity and low frequency noise becomes noticeable at high flow velocity, and a filter circuit is required to remove this noise. If the filter effect of the filter circuit is weakened, it becomes difficult to detect the vortex frequency due to noise included in the vortex signal.

On the other hand, the presence of this filter circuit makes the fluctuating lift signal inaccurate.

The present invention solves this problem.

An object of the present invention is to provide a device that can accurately measure the density or mass flow rate with a simple configuration by configuring the circuit so that the variable lift coefficient does not vary.

(Means for Solving the Problems) In order to achieve this object, the present application discloses a signal conversion circuit for converting a vortex signal from a vortex detection sensor into a signal, and high-frequency and low-frequency noise of the signal from the signal conversion circuit. Circuit for reducing the noise, a first amplifier circuit for amplifying the signal from the filter circuit, a comparator for converting the signal from the first amplifier circuit into a pulse signal, and a signal from the comparator proportional to its frequency. F / V converter for converting to DC voltage, second amplifying circuit for amplifying signal from the signal converting circuit, detection circuit for detecting signal from the second amplifying circuit, and ripple of signal from the detecting circuit A rectifying circuit for removing the component, a dividing circuit for dividing the signal from the rectifying circuit by the signal from the F / V converter circuit and outputting a pulse whose average pulse width is proportional to the measured flow rate, and the dividing circuit. Insulating means for insulating and transmitting the pulse output of the circuit, a rectifying circuit for rectifying and outputting the output of the insulating means, and when the signal from the first amplifier does not reach the set trigger level of the comparator, A switch circuit for setting the output of the division circuit to 0, the time constant of the rectification circuit and the F / V
The mass flowmeter is configured such that the time constant of the rectifier circuit of the converter is substantially the same and is higher than the beat frequency of the vortex signal.

(Operation) In the above-described configuration, the vortex signal from the vortex detection sensor is converted by the signal conversion circuit, the high frequency and low high frequency noise are reduced by the filter circuit, the signal is amplified by the first amplification circuit, and pulsed by the comparator. Convert to signal. Next, it is converted into a DC voltage proportional to the frequency of the pulse signal by the F / V comparator.

On the other hand, the signal from the signal conversion circuit is amplified by the second amplifier,
Detect with the detection circuit. Next, the rectifier circuit removes the ripple component.

The signal from this rectifier circuit is divided by the signal from the F / V converter in the divider circuit to output a pulse whose average pulse width is proportional to the measured flow rate. This output is insulated by insulating means and rectified by a rectifying circuit to obtain an electric signal corresponding to the mass flow rate.

On the other hand, when the signal from the first amplifier does not reach the set trigger level of the comparator, the output from the divider circuit is set to 0 by the gate circuit according to the signal from the F / V converter.

Examples will be described below.

(Embodiment) FIGS. 1 (A) and (B) are configuration explanatory views of an embodiment of the present invention, (A) is a front view, (B) is a side view, and FIG. 2 is a detector of FIG. It is a structure explanatory view showing a section in a section.

In the figure, 10 is a vortex flowmeter detector, and 20 is a vortex flowmeter converter.

In the vortex flowmeter detector 10, 11 is a pipe through which a measurement fluid flows, 12 is a cylindrical nozzle provided at a right angle to the pipe 11, 13
Is a columnar vortex generator inserted at a right angle into the pipe 11 through the nozzle 12, and is made of stainless steel or the like, and its upper end 131 has the nozzle 1
It is fixed to 2 by screwing or welding, and the lower end 132 is supported by the conduit 11 by a plug. The fluid-contacting portion 133 of the vortex generator 13 in contact with the measurement fluid has a Karman vortex street in the measurement fluid and has a trapezoidal cross-sectional shape, for example, so as to stably enhance the lift change. Has 134. Reference numeral 135 denotes an outer cylinder portion formed in the vortex generator 13 by the recess 134. Reference numeral 14 denotes a sensor portion, which is provided in the recess 134 of the vortex generator 13 with a first stress detection sensor 142 and a second stress detection sensor 141.
And are pressed and fixed at regular intervals.

FIG. 3 is a block diagram of the electrical circuit 30 (not shown in FIG. 2) of FIG.

31 and 32 are charge converters, which are stress detection sensors 141 and 142
The AC charges q ₁ and q ₂ detected in step 3 are converted into AC voltages E ₃₁ and E ₃₂ . Reference numeral 33 is an adder / subtractor circuit, which adds outputs from the charge converters 31 and 32 to obtain an AC voltage E ₃₃ . A second amplifier circuit 34 amplifies the AC voltage E ₃₃ into an AC voltage E ₃₄ . Reference numeral 35 is a detection circuit, which detects the AC voltage E ₃₄ and sets it as E ₃₅ . A rectifier circuit 36 removes the ripple component of the AC voltage E ₃₅ . A filter circuit 37 removes low-frequency or high-frequency noise contained in the AC voltage E ₃₃ to obtain an AC voltage E ₃₇ . A first amplifier circuit 38 amplifies the AC voltage E ₃₇ to form an AC voltage E ₃₈ .
39 is a Schmitt trigger circuit, which converts the AC voltage E ₃₈ into a pulse signal P ₃₉ of a constant level. 41 is an F / V converter, which converts the pulse signal P ₃₉ into a DC voltage E ₄₁ proportional to its frequency.
Convert to. Reference numeral 42 denotes a division circuit, which performs a desired calculation on the outputs E ₄₁ and E ₃₆ of the F / V converter 41 and the rectification circuit 36, and outputs a pulse signal P ₄₂ whose average pulse width is proportional to the measured flow rate. Four
3 is a gate circuit, the AC voltage E ₃₈ from the first amplifier circuit 38 when no longer reached the set trigger level of Schmitt circuit 39, the output of the division circuit 42 to zero. Gate circuit
43 includes a comparator 431 and a switch 432. The comparator 431 detects that the output of the F / V converter 41 becomes 0, and at this time turns on the switch 432 so as to prevent the output of the division circuit 42 from being output to a transformer (described later). Reference numeral 44 is an insulating circuit for insulating and transmitting the pulse output of the division circuit 42. In this case, a transformer is used. 45 is a rectifier circuit that rectifies the output of the transformer and outputs E ₄₄ .
Thus, the time constant of the rectifier circuit 36 and the time constant of the F / V converter 41 are made substantially the same and are set to be higher than the beat frequency of the vortex signal.

In the above configuration, in order to accurately detect the absolute value of the variable lift signal, a signal conversion circuit having a flat f characteristic within the vortex frequency band (charge converters 31, 32 and addition / subtraction circuit 33)
After the physical quantity was converted into an electric quantity by (1), it was amplified by the second amplifying circuit 34 which also has a flat f characteristic within the band of the vortex frequency, and used as it was as the input of the detecting circuit 35.

On the other hand, in the eddy frequency detection, after passing through the signal conversion circuit (charge converters 31, 32 and addition / subtraction circuit 33), in order to reduce the high frequency and low frequency noise contained in the vortex signal, the filter circuit 37 and the first amplification circuit are provided. After passing through 38, the Schmitt circuit (comparator) 39 was used as an input.

As a result of the above, by separately dividing the variable lift signal detection circuit and the vortex frequency detection circuit immediately after the signal conversion circuit,
It was possible to achieve both accurate measurement of the absolute value of the fluctuating lift signal and reliable detection of the vortex frequency.

Therefore, in the three-dimensional flow in the circular pipe, it becomes possible to accurately detect the variable lift. From the experimental results, the variable lift F _L is exactly proportional to the square of the flow velocity V ² , that is, At, the variable lift coefficient C _L = const was obtained.

Conventionally, the fluctuation lift coefficient C _L of a plough body (vortex generator) is generally very unstable even in a two-dimensional flow, and is regarded as a function such as Reynolds number Re. According to the literature mentioned above, the value of the variable lift coefficient C _L varies greatly depending on the experimenter, and even if the Strouhal number St is constant (the vortex frequency is proportional to the flow velocity), the variable lift coefficient C _L (vortex Strength)
Was not exactly proportional to the square of the flow velocity, V ² . Since the detection sensor that measures the variable lift uses strain, displacement, and force sensor, AC noise of the fluid, pipe vibration, noise of the measurement system, etc. are superimposed, making separation and detection difficult.

And Thus, West German Patent DE3032578 C2, not explicitly any fluctuation coefficient of lift C _L detected at No. Sho 57-61916, assuming variation coefficient of lift C _L is constant, which was discussed known techniques is there.

On the other hand, it has been clarified that the average drag becomes almost constant when the Reynolds number Re> 2,000 or more, as shown in literature values. This is because the average drag force can be detected as a direct current component, so that the measuring circuit can completely remove the alternating current noise component, and accurate measurement can be performed without special measures.

Next, when the signal from the first amplifier circuit 38 does not reach the set trigger level of the Schmitt circuit 39, the division circuit
A gate circuit 43 for setting the output of 42 to 0 is provided. When the vortex signal becomes small and the set trigger level of the Schmitt circuit 39 is not reached, the pulse output P from the Schmitt circuit 39
₃₉ is not output, and as a result, the output of the F / V converter 41 becomes 0. On the other hand, the rectifier circuit 36 of the variable lift detection circuit
The output voltage E ₃₆ of does not become 0 due to noise in the flow of the measurement fluid, circuit noise, or the like. Therefore, the denominator input of the division circuit 42 is 0, and the numerator input is not 0, resulting in a large + error. The gate circuit 43 uses the output voltage of the F / V converter as the gate signal voltage and performs zero cut to cut this error. Fig. 4 shows the relationship between the output Eo and ρV.

The setting trigger level of the Schmitt circuit 39 is S / N =
It is set to 1 or a slightly larger value. S / N <
This is because if the value becomes 1, the vortex frequency can be detected by the filter circuit 37, but a large error occurs in the measurement of the variable lift.

Next, the input to the division circuit is the analog voltage proportional to V ² from the rectifier circuit 36 and the analog voltage proportional to V from the F / V converter, and the output has an average pulse width proportional to the measured flow rate. Since it is a pulse train, the insulation by the transformer 44 can be performed easily and inexpensively, and the common mode noise generated in the field can be prevented.

Further, since the time constants of the rectifier circuit 36 and the F / V converter 41 are substantially the same and are configured to be higher than the beat frequency of the vortex signal, even with respect to fluctuations in the measurement flow rate of the measurement fluid. What can be accurately followed is obtained.

The detection circuit 35 may be half-wave rectification or double-wave rectification. The noise superimposed on the input signal E ₃₄ of the detection circuit 35 is S / N.
If> 1, the effect of noise is reduced. For example,
As shown in FIG. 5 (A), the detection waveform E ₃₅ of the input signal E ₃₄ in which high frequency noise is superimposed on the low frequency signal is a waveform in which noise is superimposed as shown in FIG. 5 (B). However, for example, regarding A and B shown in FIG. 5B, the noise is averaged and the noise is reduced as a whole. or,
Noise can be almost completely removed by synchronous rectification at the vortex frequency.

The insulating means by the transformer 44 can also be obtained by other insulating means such as a photocoupler.

By the way, the stability of vortex shedding (stability of lift) is considerably poor even if the straight pipe length is sufficient, and the fluctuation is several tens% or more. Therefore, the amplitude of the output of the detection circuit 35 varies considerably, and even if the time constant of the rectifier circuit 36 is sufficient for the frequency of the vortex, the ripple is large and not practical. The time constant is the detection circuit
One must consider the fluctuating frequency of the output amplitude of 35. Judging from the test results in water, this value is 5 seconds
The above is necessary.

On the other hand, in order to improve the stability of lift, it is necessary to stabilize the flow, and it is effective to install a rectifying device such as a rectifying tube or a perforated plate on the upstream side of the vortex generator 13.

FIG. 6 and FIG. 7 show a concrete structure of the electric circuit of FIG.

In the figure, OP1 and OP2 are operational amplifiers that form the charge converters 31 and 32, and are the first and second stress detection sensors 141 and 142.
The generated charges q ₁ and q ₂ are converted into a low impedance AC voltage. Here, in the capacitor C ₁ = C _2, resistors R ₁ = R _2, and C ₁
The constant is selected so that the corner frequency f _C of the high pass filter composed of R ₁ , C ₂ and R ₂ is sufficiently smaller than the lower limit of the vortex signal frequency. OP3 is an operational amplifier that constitutes the adder / subtractor circuit 33, and removes vibration noise. Adjust constant λ with variable resistor R ₄ . OP4 is an amplifier which constitutes the second amplifier circuit 34, and OP5 and OP6 are operational amplifiers which constitute the detection rectification circuits 35 and 36. C ₃ and C ₄ are coupling capacitors, the constants of which are selected so that the impedance is sufficiently small for the vortex signal frequency. R ₅ and C ₅ are time constants of the rectifier circuit, are equal to the time constants of the rectifier circuits R ₁₇ and C ₁₂ of the F / V converter, and are selected to be values sufficient to reduce ripples.

OP7 is divided amplifier for obtaining a predetermined input voltage to the division circuit 42 by adjusting the resistance R _6. OP8 and OP9 are operational amplifiers composed of a filter circuit 37 and a first amplifier circuit 38, which remove high-frequency and low-frequency noise contained in the output of the adder-subtractor circuit 33, and reduce the vortex signal to the Schmitt trigger circuit 39 of the next stage.
The input signal of is also amplified. C ₆ , C ₇ , C ₈ , R ₇ , R ₈ , R
₉ is a capacitor and resistor that form a bandpass filter, C
₉ , C ₁₀ , C ₁₁ , R ₁₀ , R ₁₂ , and R ₁₃ are also capacitors and resistors that form a bandpass filter. D ₁ and D ₂ are Zener diodes for canceling the low-pass filter composed of C ₁₁ and R ₁₃ and limiting the amplitude when the signal level becomes high. OP ₁₀ is an operational amplifier that constitutes the Schmitt circuit 39, and the width of hysteresis is determined by R ₁₄ , R ₁₅ , and R ₁₆ . OP ₁₁ is F
An operational amplifier that amplifies the output of the / V converter 41 to a predetermined input voltage of the division circuit 42 and adjusts with R ₁₈ . OP ₁₂ is 7th
As shown in the figure, the zero-cut setting voltage is set by the voltage dividing ratio of R ₂₅ and R ₂₆ of E ₁ , and is a comparator that obtains a control voltage for turning on / off the output of the inverting amplifier circuit 46 in the transistor of Q 2.

OP13, OP14, are operational amplifiers that constitute the division circuit 42.
The part constituted by OP14 is an integrating circuit, and the part constituted by OP14 is a comparator. DC input with this configuration
E _2, dividing circuit is constructed the pulse duty factor proportional to E ₂ / E ₃ of E ₃ is output. The arithmetic circuit 44 uses this output pulse to perform signal transmission. OP15 is an inverting amplifier circuit 46
The pulse output from the division circuit 42 is inverted and sent to the isolation circuit 44 by the operational amplifier that constitutes the. T1 is a transformer that constitutes the insulating circuit 44, and the transistor Q3 is turned on by the pulse signal from the inverting amplifier circuit 46, and the power source E ₄ is added to the blocking oscillator circuit configured by the transistor Q4 to start oscillation (high frequency). This oscillation signal is transmitted to transistor Q5 by T1.
, The transistor Q5 cannot follow the oscillation signal, and when the blocking oscillator circuit oscillates, it turns on.
Turns off when oscillation stops.

Rectifier circuit 45 with inverter U1, resistor R27, and capacitor C14
Are configured. Inverter U1 operates with stabilized power supply (E _5), it has a peak value constant by inverting the on and off of the transistor Q5. The output pulse of the inverter U1 is the output pulses the duty ratio of the dividing circuit 42 is the same, thus DC output proportional to E ₂ / E ₃ by smoothing the pulse at resistor R27 and capacitor C14 is obtained . The time constant of the resistor R27 and the capacitor C14 is set to a value that can sufficiently smooth the output pulse of the division circuit 42.

In the block diagram of FIG. 3, the filter circuit 37, the first circuit
Although shown separately from the amplifier circuit 38 according to their functions, FIG. 6 shows an active filter using operational amplifiers OP8 and OP9. Also, the gate circuit in FIG.
In FIG. 7, it is composed of a comparator OP12 and a transistor Q2. Fig. 8 shows the circuit of Fig. 6 with a flow velocity of 0.4m.
It is an output waveform example when the actual flow test of water of / s is performed.

As shown in FIG. 8, the output waveform (A) of the charge converter 31 (point (A) in FIG. 6) has a vortex signal and pipe vibration noise, and the output waveform (B) of the charge converter 32 (see FIG. Pipe line vibration noise appears at point (B) in FIG. Output waveform (C) of the adder / subtractor circuit 33 ((C) of FIG. 6)
The point) is a waveform from which the pipeline vibration noise is removed, and the input waveform (D) of the Schmitt circuit 39 (point D in FIG. 6) is a waveform with a significantly improved S / N ratio due to the high cut filter effect. It is shown.

This waveform example is for a low flow velocity, but at high flow velocity, low frequency noise is superimposed on the vortex signal or a beat waveform appears in the vortex signal itself, and it is mainly to improve the S / N ratio by the low cut filter effect. You can

As a result of the actual flow rate test with water, as shown in FIG.
It was confirmed that the output of the rectifier circuit 36 was proportional to the square of the flow velocity within an error range of ± 1%. It has also been confirmed that the lift between air and water is proportional to the density ρ.

In the above-described embodiment, the so-called stress detection method for detecting the alternating stress of the vortex shedder fixed at one end and supported at one end has been described. It may be one that detects stress.

In addition, another force detection method for detecting the variable lift, for example,
Even in the case of displacement, strain, torque, etc., if the mechanical constants (Young's modulus, spring constant) of the sensor due to temperature changes are temperature-compensated, a mass flowmeter using Karman vortices can be constructed.

(Effects of the Invention) As described above, the present application has a signal conversion circuit that converts a vortex signal from a vortex detection sensor, a filter circuit that reduces high-frequency and low-frequency noise of a signal from the signal conversion circuit, A first amplifier circuit that amplifies the signal from the filter circuit, a comparator that converts the signal from the first amplifier circuit into a pulse signal, and an F / that converts the signal from the comparator into a DC voltage proportional to its frequency. A V converter, a second amplifier circuit that amplifies the signal from the signal conversion circuit, a detection circuit that detects the signal from the second amplifier circuit, and a rectification circuit that removes the ripple component of the signal from the detection circuit. Insulating the pulse output of the division circuit from the division circuit that divides the signal from the rectifier circuit by the signal from the F / V converter circuit and outputs a pulse whose average pulse width is proportional to the measured flow rate. And a rectifying circuit for rectifying and outputting the output of the insulating means, and an output of the dividing circuit when the signal from the first amplifier does not reach the set trigger level of the comparator. And a switch circuit for making the time constant of the rectifier circuit and the time constant of the rectifier circuit of the F / V converter substantially the same, and to be larger than the beat frequency of the vortex signal. Since the flowmeter is configured, the fluctuation lift signal detection circuit and the vortex frequency detection circuit are separately separated immediately after the signal conversion circuit, so that the absolute value of the fluctuation lift signal can be accurately measured and the vortex frequency can be reliably measured. It is possible to achieve both detection and detection.

Further, since the gate circuit that sets the output of the division circuit to 0 when the signal from the first amplifier does not reach the set trigger level of the comparator is provided, a large error is prevented near the flow rate of 0. can do.

Further, since the output of the division circuit is a pulse train in which the average of the pulse width is proportional to the measured flow rate, insulation by a transformer is easy and inexpensive, and common mode noise generated in the field can be prevented.

Also, since the time constants of the time constant circuit and F / V converter are set to be almost the same and the beat frequency of the vortex signal is set to be greater than that of the vortex signal, it is possible to obtain a device that can accurately follow the change in mass flow rate. To be

As described above, according to the present invention, with a simple configuration,
It is possible to realize an apparatus capable of accurately measuring the density or the mass flow rate.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of an embodiment of the present invention, (A) is a front view, (B) is a side view, and FIG. 2 is a structural explanatory view showing the detector section of FIG. 1 in section. FIG. 3 is an electric circuit diagram of FIG. 1, FIGS. 4 and 5 are operation explanatory diagrams of FIG. 3, FIGS. 6 and 7 are concrete configuration explanatory diagrams of FIG. 3, and FIG. 6 and 7, the output waveform diagram of each part when the actual flow test of water with a flow velocity of 0.4 m / s is conducted, and Fig. 9 is the output characteristic diagram of the rectifier circuit of Fig. 7, Fig. 10 Figure is an explanatory view of the lift force and the like when the vortex generator is arranged in the pipeline, FIG. 11 is a structural explanatory view of a conventional example generally used from the past, FIG. 12 is a component explanatory view of FIG. 11, FIG. 13 is a characteristic explanatory diagram of drag coefficient, FIG. 14 is a characteristic explanatory diagram of Strouhal number, and FIG. 15 is an explanatory diagram of lift coefficient. 10 …… Vortex flow detector, 11 …… Pipe, 12 …… Nozzle, 13…
… Vortex generator, 131 …… Upper end, 132 …… Lower end, 133 …… Wetted part, 134 …… Recessed part, 135 …… Outer cylinder part, 14 …… Sensor part, 140 …… Piezoelectric element, 141 …… No. 2 stress detection sensor,
142 …… First stress detection sensor, 20 …… Vortex flowmeter converter, 30 …… Electric circuit, 31,32 …… Charge converter, 3
3 ... Addition / subtraction circuit, 34 ... Second amplification circuit, 35 ... Detection circuit, 36 ... Rectification circuit, 37 ... Filter circuit, 38 ... First
Amplification circuit, 39 ... Schmidt trigger circuit, 41 ... F / V converter, 42 ... Division circuit, 43 ... Gate circuit, 431 ...
… Comparator, 432 …… Switch, 44 …… Insulation circuit, 4
5 ... Rectifier circuit.

Claims (1)

[Claims] 1. A signal conversion circuit for converting a vortex signal from a vortex detection sensor into a signal, a filter circuit for reducing high frequency and low frequency noise of the signal from the signal conversion circuit, and an amplification of the signal from the filter circuit. A first amplifier circuit, a comparator for converting the signal from the first amplifier circuit into a pulse signal, an F / V converter for converting the signal from the comparator into a DC voltage proportional to its frequency, and the signal conversion circuit A second amplifying circuit for amplifying the signal from the second amplifying circuit, a detecting circuit for detecting the signal from the second amplifying circuit, a rectifying circuit for removing a ripple component of the signal from the detecting circuit, and a signal from the rectifying circuit for A division circuit that outputs a pulse whose average pulse width is proportional to the measured flow rate divided by the signal from the F / V converter circuit, an insulating means that insulates and transmits the pulse output of the division circuit, and the insulation A rectifying circuit for rectifying and outputting the output of the stage; and a switch circuit for setting the output of the dividing circuit to 0 when the signal from the first amplifier does not reach the set trigger level of the comparator. A mass flowmeter in which the time constant of the rectifier circuit and the time constant of the rectifier circuit of the F / V converter are made substantially the same and which is higher than the beat frequency of the vortex signal.